To make their case, lawmakers are citing the 1973 War Powers Resolution. Passed after President Richard Nixon's secret Vietnam War-era operations, the law reaffirmed Congress' constitutional responsibility to declare war and put a 60-day time limit on the president's ability to take unauthorized, emergency military action. Since then, presidents of both parties have maintained that the resolution is unconstitutional and have regularly disregarded it.
After a decade of costly and deadly fighting in the Muslim world, Americans strongly oppose any new U.S. war in the region. Opinions in Congress are mixed as well. Republicans are split between hawks and tea party isolationists. Democrats are divided between advocates of humanitarian intervention and those who fear that even limited action risks sucking the United States into another conflict.
Sen. Tim Kaine of Virginia, a former Democratic Party chairman, said the Assad government must be held accountable for its "despicable" chemical attacks. But he urged that proper procedures be followed.
"Absent an imminent threat to United States national security, the U.S. should not be engaged in military action without congressional approval," Kaine said.
Sen. Bob Corker of Tennessee, the top Republican on the Foreign Relations Committee, has made a similar argument.
Sen. John Cornyn, R-Texas, asked only that Obama present his case to the American people and consult with Congress. "He needs to explain what vital national interests are at stake and should put forth a detailed plan with clear objectives and an estimated cost for achieving those objectives," he said.
That doesn't seem near enough for tea party favorite Rep. Justin Amash, R-Mich., who has issued a series of tweets arguing that unauthorized strikes against Syria would be unconstitutional and illegal. He is putting pressure on leadership in his own party to call Congress back into session for a debate and vote before any such action occurs.
Rep. Peter King, R-N.Y., is on the opposite end of the spectrum. "I think the president has the right to attack without the approval or consultation of Congress," he said. "But a wise leader would reach out."
Lawmakers are scheduled to return from a five-week recess on Sept. 9.